JP2010003549A - Electrode catalyst for fuel cell, its manufacturing method, and fuel cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly active electrode catalyst for a fuel cell replacing platinum and having high four-electron reduction performance, and its manufacturing method. <P>SOLUTION: The method of manufacturing the electrode catalyst for the fuel cell represented by M<SB>1</SB>M<SB>2</SB>X (M<SB>1</SB>is Ru, M<SB>2</SB>is Fe and/or Ni, and X is at least one kind of chalcogen element) has processes for mixing alcohol and water with at least one kind of compound selected from an Fe nitric acid compound, an Ni nitric acid compound, an Fe hydrochloric acid compound and an Ni hydrochloric acid compound; adding an Ru chalcogen compound while agitating a mixture; adding a reducing agent while agitating the mixture to reduce the Fe and/or Ni compound; filtering and washing a product; and heat-treating the filtered object. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a novel electrode catalyst for fuel cells excellent in initial activity and durability, which is a substitute for a conventional platinum catalyst, a method for producing the same, and a fuel cell using the same.

  Platinum or a platinum alloy-based catalyst is mainly used as the anode catalyst for the polymer electrolyte fuel cell. Specifically, a catalyst in which a noble metal including platinum is supported on carbon black has been used. Platinum-supported carbon black is obtained by adding sodium hydrogen sulfite to a chloroplatinic acid aqueous solution, reacting with hydrogen peroxide solution, adsorbing the resulting platinum colloid to carbon black, washing, and heat-treating as necessary. The preparation method is general. In a polymer electrolyte fuel cell, platinum-supported carbon black is dispersed in a polymer electrolyte solution to form a paste. The paste is applied to a gas diffusion electrode such as carbon paper, dried, and then dried with two gas diffusion electrodes. An electrolyte membrane-electrode assembly (MEA) is manufactured by sandwiching a molecular electrolyte membrane and performing hot pressing.

  One of the problems in putting a polymer electrolyte fuel cell into practical use is material cost. One means for solving this is to reduce the amount of platinum.

On the other hand, it is known that when oxygen (O ₂ ) is electrolytically reduced, superoxide is generated by one-electron reduction, hydrogen peroxide is generated by two-electron reduction, and water is generated by four-electron reduction. In a fuel cell stack using platinum or a platinum-based catalyst as an electrode, if a voltage drop occurs for some reason, the 4-electron reducibility is reduced and the 2-electron reducibility is obtained. For this reason, hydrogen peroxide is generated, which causes deterioration of MEA.

  Recently, a low-cost fuel cell catalyst that does not require an expensive platinum catalyst has been developed by a reaction in which oxygen is reduced by four electrons to generate water. Non-Patent Document 1 below discloses that a catalyst having a chalcogen element is excellent in 4-electron reducibility and suggests application to a fuel cell.

  Similarly, Patent Document 1 below discloses an electrode catalyst composed of at least one transition metal and a chalcogen as a platinum substitute catalyst, wherein Ru is used as the transition metal, and S or Se is used as the chalcogen. Yes. Here, it is disclosed that the Ru: Se molar ratio is in the range of 0.5 to 2 and the stoichiometric number n of (Ru) nSe is 1.5 to 2.

  Patent Document 2 listed below discloses a fuel cell catalyst material having a transition metal selected from Fe or Ru, a nitrogen-containing organometallic transition complex, and a chalcogen component such as S as a Pt substitute catalyst. .

  Non-Patent Document 1 below discloses a Mo—Ru—Se ternary electrode catalyst and a synthesis method thereof.

  Furthermore, Non-Patent Document 2 below discloses Ru-S, Mo-S, Mo-Ru-S binary and ternary electrode catalysts, and a synthesis method thereof.

  Further, Non-Patent Document 3 below discloses Ru—Mo—S and Ru—Mo—Se ternary chalcogenide electrode catalysts.

JP-T-2001-502467 JP-T-2004-532734 Electrochimica Acta, vol. 39, no. 11/12, pp. 1647-1653, 1994 J. et al. Chem. Soc. Faraday Trans. , 1996, 92 (21), 4311-4319. Electrochimica Acta, vol. 45, pp. 4237-4250, 2000

  The catalysts described in Patent Document 1 and Non-Patent Documents 1, 2, and 3 are not sufficient in activity and four-electron reduction performance.

  The present inventors have found that the above problems can be solved by setting the loading ratio of the binary chalcogen-based catalyst or the ternary chalcogen-based catalyst within a specific range, and have reached the present invention.

  That is, first, the present invention is an invention of a fuel cell electrode catalyst containing at least one transition metal element and at least one chalcogen element, and is defined by catalyst weight / (catalyst weight + carrier weight). It is characterized in that the loading ratio on the carrier is 6 to 32%, preferably 10 to 20%.

  An electrode catalyst for a fuel cell that is an object of the present invention is a fuel cell electrode catalyst containing at least one transition metal element and at least one chalcogen element, and is a binary chalcogenide catalyst or a ternary or higher catalyst. It is a chalcogenide catalyst. Specifically, those disclosed in the above patent documents and non-patent documents are targeted. Among these, chalcogenide catalysts represented by the general formula RuX (X is at least one chalcogen element) are preferably exemplified.

  The chalcogen element of the chalcogenide catalyst of the present invention is preferably at least one selected from sulfur (S), selenium (Se), and tellurium (Te).

  Secondly, the present invention relates to an electrode catalyst for a fuel cell comprising at least one transition metal element and at least one chalcogen element which is heat-treated after mixing, reducing, and reducing the transition metal element species, the chalcogen element species and the support. The transition metal element species and the chalcogen element species so that the loading ratio on the carrier defined by catalyst weight ÷ (catalyst weight + carrier weight) is 6 to 32%, preferably 10 to 20%. And a carrier.

  The types of chalcogenide catalysts used in the method for producing an electrode catalyst for fuel cells of the present invention, preferred specific examples of chalcogenide catalysts, and examples of chalcogen elements are as described above.

The chalcogenide catalyst of the present invention is preferably heat-treated, specifically, heat treatment at 400 to 600 ° C. for 10 minutes to 5 hours, more preferably 480 to 520 ° C. for 30 minutes to 2 hours.
3rdly, this invention is a fuel cell provided with said electrode catalyst for fuel cells.

  The fuel cell electrode catalyst of the present invention and the fuel cell electrode catalyst produced by the method of the present invention have high four-electron reduction performance and high activity compared to conventional transition metal-chalcogen element-based catalysts, It can replace the conventional platinum catalyst.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.
[Example: Preparation of catalyst]
In this example, Ru ₃ (CO) ₁₂ , Se or S, xylene, carbon black was used as a raw material, and the heat treatment temperature dependence of the oxygen reducing ability was examined using the following synthesis method.
(1) The above raw materials are mixed and a reflux synthesis method (wet chemistry, organic low temperature synthesis) is used. At this time, as a cathode carrier (porous support), for example, carbon black was immersed in the above mixture solution to carry the catalyst.
(2) The obtained product was filtered and washed, and vacuum-dried at 50 to 100 ° C.
(3) Further heat treatment was performed.

  It is generally said that the performance of a fuel cell electrode catalyst increases as the surface area per unit weight increases when compared with the same weight. In the binary chalcogenide and ternary chalcogenide proposed in the present invention, increasing the surface area per unit weight is a problem for improving performance.

  The fuel cell electrode catalyst is used by being supported on a carrier such as carbon black. It is known from Patent Document 1 that the particle size of the binary chalcogenide MX (M: Ru, XS or Se) is 3 to 4 nm. However, when it is supported on a carrier having a finite surface area, it is generally said that in the case of a high loading amount, secondary particles are formed by aggregation of the particles of each other, and the surface area of the catalyst is reduced and the performance is lowered. Yes.

  Therefore, in this example, among the binary chalcogenide MX (M: transition metal, X: chalcogen element), an optimum loading rate is defined for a catalyst in which M is Ru and X is S or Se. The results are shown in FIG.

From the results of FIG. 1, it is understood that the loading rate defined by catalyst weight ÷ (catalyst weight + carrier weight) is preferably 6 to 32%, more preferably 10 to 20%.
The performance evaluation method was performed as follows.

[Evaluation equipment]
As shown in FIG. 2, the evaluation was carried out using a three-electrode electrochemical cell. As the electrolytic solution, 0.1 mol / L perchloric acid was used. A silver-silver chloride electrode was used as the reference electrode.

[Electrode fabrication method]
FIG. 3 shows an electrode manufacturing method. Catalyst ink was blended in such a way that Nafion was 0.1 with respect to 1 by weight. The ink composition is 0.05 g of catalyst, 1.0 g of 0.5 wt% Nf solution, and 2.0 g of ethanol. (1) Mix with Nf solution and ethanol, (2) Disperse with ultrasonic waves, (3) Drop catalyst ink onto glassy carbon disk electrode and let it dry naturally.

[Evaluation procedure]
Table 1 shows the current evaluation procedure. The electrode rotation speed in Table 1 below indicates the rotation speed of the working electrode in FIG. The index representing the activity is oxygen reduction current = (reduction current measured by O ₂ electrochemical measurement in Table 1) − (reduction current measured by N ₂ electrochemical measurement in Table 1).

  The fuel cell electrode catalyst prepared so that the loading ratio on the carrier defined by the catalyst weight / (catalyst weight + carrier weight) of the present invention is 6 to 32%, preferably 10 to 20%, Compared to transition metal monochalcogen element-based catalysts, it has a high four-electron reduction performance, is highly active, and can replace platinum catalysts. This contributes to the practical application and spread of fuel cells.

The relationship between the loading rate defined by catalyst weight ÷ (catalyst weight + carrier weight) and power generation performance is shown. An evaluation apparatus is shown. An electrode manufacturing method will be described.

Claims (11)

  An electrode catalyst for a fuel cell comprising at least one transition metal element and at least one chalcogen element, wherein the loading ratio on the carrier defined by catalyst weight ÷ (catalyst weight + carrier weight) is 6 to 32%. An electrode catalyst for a fuel cell, characterized in that   2. The fuel cell electrode catalyst according to claim 1, wherein the loading ratio is 10 to 20%.   2. The fuel cell electrode catalyst comprising at least one transition metal element and at least one chalcogen element is represented by the general formula RuX (X is at least one chalcogen element). Or the electrode catalyst for fuel cells of 2 or 2.   4. The fuel cell electrode catalyst according to claim 1, wherein the chalcogen element is at least one selected from sulfur (S), selenium (Se), and tellurium (Te). 5. .   A method for producing an electrode catalyst for a fuel cell comprising at least one transition metal element and at least one chalcogen element, wherein the transition metal element seed, the chalcogen element seed, and the support are mixed, reduced, and heat-treated. A fuel cell electrode catalyst comprising a transition metal element species, a chalcogen element species, and a carrier so that the loading ratio on the carrier defined by weight ÷ (catalyst weight + carrier weight) is 6 to 32%. Manufacturing method.   The method for producing an electrode catalyst for a fuel cell according to claim 5, wherein the loading ratio is 10 to 20%.   6. The fuel cell electrode catalyst containing at least one transition metal element and at least one chalcogen element is represented by the general formula RuX (X is at least one chalcogen element). Or a method for producing an electrode catalyst for a fuel cell according to 6.   The fuel cell electrode catalyst according to any one of claims 5 to 7, wherein the chalcogen element is at least one selected from sulfur (S), selenium (Se), and tellurium (Te). Manufacturing method.   The method for producing a fuel cell electrode catalyst according to any one of claims 5 to 8, wherein the heat treatment is performed at 400 to 600 ° C for 10 minutes to 5 hours.   The method for producing an electrode catalyst for a fuel cell according to any one of claims 5 to 8, wherein the heat treatment is performed at 480 to 520 ° C for 30 minutes to 2 hours.   A fuel cell comprising the fuel cell electrode catalyst according to claim 1.

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